Which is the oldest observatory?

Copenhagen, Denmark is the oldest observatory. Kobenhavns University Astronomical Observatory (Copenhagen University Observatory) on Ostensible is an astronomical observatory owned and operated by Copenhagen University. It is located in Copenhagen, Denmark, and has been in operation since 1861. Copenhagen is the capital and largest city of Denmark, with an urban population of 1,181,239 (2010) and a metropolitan population of 1,914,865 (2011).